Method and apparatus for suction dredging

ABSTRACT

The relatively hard layer of clay which covers an underwater body of sand is penetrated rapidly by forcing the lower end of a suction-dredging pipe assembly into the layer while drawing water through the pipe at a sufficiently rapid rate as to erode the clay and form a core of clay in the lower end of the pipe. This core may be removed either by crushing same so that the flowing water rapidly washes it away, or by periodically maintaining suction on the pipe to retain the core, withdrawing the pipe from the hole and expelling the core, whereafter the operation is repeated until the body of sand is reached.

United States Patent Inventor Jan De Koning Amsterdam, Netherlands Appl, No. 765,416 Filed Oct. 7, 1968 Patented June 22, 1971 Y Assignee N. V. lngenieursbureau voor Systemen en Octmoien Spanstaal Rotterdam, Netherlands Priority Oct. 16, 1967 Netherlands 67.14007 METHOD AND APPARATUS FOR SUCTION DREDGING 11 Claims, 10 Drawing Figs.

US. Cl 37/57, 37/58, 37/61, 37/195, 175/6, 175/20, 175/405, 302/15, 302/58 Int. Cl E021 3/92, E02f 3/94 Field ofSeareh 37/57,58,

References Cited UNITED STATES PATENTS 336,619 2/1886 Badger 6l9,727 2/1899 Davis 8/ 1900 Munn 37/63 1,758,047 5/1930 Jensen 37/62 1,964,951 7/1934 Kertzman 37/57 X 2,774,569 12/ l 956 Jacobsen 37/63 3,153,290 10/1964 Saito 37/62 3,163,241 12/1964 Daigle et al..... 175/20 X 3,273,930 9/ 1966 Gottfried 175/405 X FOREIGN PATENTS 837,669 6/1960 Great Britain 37/58 6,501,404 8/1966 Netherlands 37/58 6,501,405 8/1966 Netherlands 37/58 6,604,227 10/ l 967 Netherlands 37/58 Primary Examiner-Robert E. Pulfrey Assistant Examiner-Clifford D. Crowder Attorney-Snyder and Butrum ABSTRACT: The relatively hard layer of clay which covers an underwater body of sand is penetrated rapidly by forcing the lower end of a suction-dredging pipe assembly into the layer while drawingv water through the pipe at a sufficiently rapid rate as to erode the clay and form a core of clay in the lower end of the pipe. This core may be removed either by crushing same so that the flowing water rapidly washes it away, or by periodically maintaining suction on the pipe to retain the core,

withdrawing the pipe from the hole and expelling the core,

PATENTED JUN22 I9?! 35 5, 73

SHEET 2 OF 3 FIG.4

INVENTOR JAN DE Kom'ue BY V MkM ATTORNEYS PATENTED JUN22 1971 SHEET 3 OF 3 INVENTOR TAN DE Kohl/Mg ATTORNFYS METHOD AND APPARATUS FOR SUCTION DREDGING The invention relates to a suction-dredging installation for sucking up sand, comprising a pump and a suction pipe which is connected to the pump and has a grid for retaining large objects, such as stones, found in the soil. The invention also relates to a method for sucking up sand by means of such a suction-dredging installation, wherein the suction pipe is inserted into the soil. Such a suction dredging installation and such a method are known. The insertion of the suction pipe into the soil is difficult, if the layer of sand to be sucked up is covered by an upper layer of clay or some other highly cohesive material. The insertion of the suction pipe through the upper layer causes a lot of unproductive time. The invention has the object to shorten this unproductive initial period and provides to this end an improved suction-dredging installation characterized in that the grid is movable between an extended and retracted position in which the grid is disposed outside and inside the suction pipe respectively. In the new method to be performed by means of the suction-dredging installation according to the invention, the suction pipe, with the grid retracted, is so inserted into the firm soil, that a large portion of soil which has not yet be fluidized penetrates into the suction pipe. This portion of soil can be conveniently removed from the suction pipe by the two preferred methods described hereinafter with reference to a drawing.

In the diagrammatic drawings:

FIGS. 1, 2 and 3 show sketches of the situation during the performance of a method according to the invention;

FIGS. 4 and 5 show sketches of the situation during the performance of a further developed method according to the invention;

FIG. 6 shows a sketch of the situation during the cleaning of the grid;

FIG. 7 is a cutaway side elevation of the lower member of the suction pipe of a further developed suction-dredging installation according to the invention, and

FIGS. 8, 9 and 10 are sections, taken respectively over lines b-b, c-c, d-d in FIG. 7.

The drawings show a layer of sand 10 to be sucked up, a superjacent layer of clay 11, water 12 being thereabove, and a suction pipe 13 of a suction-dredging installation according to the invention. The suction pipe 13 comprises an inner pipe 14 connected to a pump and movably attached to a vessel (not shown); a jacket 15 enclosing the inner pipe 14 and being rigidly attached thereto; and a sliding pipe 17 fitted axially slidably in the inner pipe 14, driven by means of hydraulic cylinders 16, and having at its lower end a grid in the form of a strainer 18.

At the start of the method according to the invention, with the sliding pipe 17 retracted, the jacket 15 of the suction pipe 13 is forced into the clay layer, said jacket preferably having a sharp lower edge (cf. FIG. 1). During this operation a large portion of clay 19 penetrates into the lower end of the suction pipe 13. The arrows 24 in FIGS. 1 and 3 show how the water flows down along the outside of the jacket 15, bends around the lower edge 20, and finally flows up between the portion 19 of soil and the inner wall of the jacket 15 into the strainer 18. As a result of causing the lower edge 20 constantly to follow the bottom of the cylindrical cavity scoured out, the width of the gap at the location of the lower edge 20 and the bottom 25 is very small, and therefore the local speed of the flow of water very high, so that this flow of water quickly scours out the firm soil below the lower edge 20. After a portion of clay 19 has penetrated to a considerable extent into the suction pipe, the suction pipe 13 is drawn up and moved to one side of the hole 21, while the sliding pipe 17 is moved downwards. The strainer 18 then exerts a downward pressure on the portion of clay 19. The portion of clay 19 then drops down beside the hole 21 (cf. FIG. 2). The suction pipe 13 is then reinserted into the hole 21 and forced further into the clay layer 11. It is not disadvantageous if the suction pipe is inserted inaccurately into the hole 21. FIG. 3 shows how in this situation a fairly small portion of clay 22 and a large portion of clay 23 are removed. This operation is repeated until the suction pipe has reached the sand layer 10. The suction pipe is then continuously kept in the sand layer for sucking up the sand required.

During removal of the portions of clay l9 and 23 respectively, normal suction is constantly performed, so that the portion of clay 19 which has penetrated into the lower end of the suction pipe 13 remains in the pipe as the suction pipe 13 is lifted out of the hole 21. Instead of being vertically inserted into the clay layer 11, the suction pipe 13 can be also inserted slantingly thereinto. During the performance of the method described before, the vessel carrying the suction pipe 13 is firmly connected to anchors by cables. Preferably, this vessel has an indicating device for showing the position of the suction pipe 13. Although the suction pipe 13 can consist of just one member pivotably mounted in relation to the vessel, it preferably consists of a plurality of members, so that when the suction pipe 13 is inserted into the hole 21, a number of operations can conveniently be performed by the end of the suction pipe 13, without having to move the vessel. During the operation of forcing the suction pipe into the clay layer, the cable winches may be used to obtain a large pressure force.

A further developed method according to FIGS. 4, 5 and 6 is described with the application of a suction pipe as shown in FIG. 7, which will be described first.

FIG. 7 shows just the lower member of a suction pipe 33, which is pivotally attached in known manner to a top member thereof, which is pivotally suspended from a vessel. The lower member of the suction pipe 33 consists mainly of an inner pipe 34 connected via the top member to a sand pump which, for example, is submerged 10 meters below the water level; a jacket 35 enclosing the inner pipe 34 and rigidly attached thereto; and a long sliding pipe 37, which is disposed axially slidably in the inner pipe 34, is driven by a number of hydraulic cylinders 36, for example three, and which has a strainer 38 at its lower end, said strainer forming the grid for retaining large objects, such as stones, occurring in the soil, and having a front grid 44 extending transversely of the pipe and a cylindrical grid 41 connected thereto. The outside diameter of the cylindrical grid 41 corresponds with the inside diameter of the slightly narrowed end 39 of the jacket 35, so that when the sliding pipe 37 is retracted into the jacket end 39 the lower edge 40 of said end 39 scrapes off the large objects possibly sticking to the cylindrical grid 41. Internally, the cylindrical grid 41 communicates with the sliding pipe 37 by means of a throat 42 which tapers in the direction of flow. The outside of the cylindrical grid 41 adjoins the guide pipe 43 which slides in the jacket end 39. Between the lower end of the sliding pipe 37 and the guide pipe 43 is a cylindrical space .45 which at the top communicates with the cylindrical space 46 between the jacket 35 on the one hand and the sliding pipe 37 and the inner pipe 34 on the other hand, the said latter space communicating with a pressure water supply 47 connected to a pressure water pump, the operative pressure of said water being adjustable. At the front end the throat 42 has three peripherally distributed apertures through which the pressure water can pass from space 46 into strainer 38.

The jacket 35 has a portion 48 having a larger cross section to receive the cylinders 36. In order that the suction pipe 33 can be kept as thin as possible at the lower end, the inner pipe 34 is made relatively short and the sliding pipe 37 very long, e.g. 20 m., while the length of travel of the sliding pipe is only 4 m. The advantage of this is that the hole which is required to be formed in the firm soil is made narrower as a result of the thin suction pipe 33. Also, in the event that the sand caves in on the pipe, the load on the thinner suction pipe 33 is less. The risk of the sand reaching the long hydraulic cylinders 36 is also reduced with the suction pipe 33.

Guide ridges 49 are provided to guide the long sliding pipe 37 with respect to the jacket 35.

For insertion into the soil, the suction pipe 33 has a sharp lower edge 40 while as a result of the retractable throat 42 at the end of the sliding pipe 37 the resistance to flow into the suction'pipe 37 is low, because the flow cross section at that place is relatively considerable. When the suction pipe is inserted into the hard layer 50 of clay (see FlG. d), the supply of pressure water 47 is shut off, the sliding pipe 37 is kept with the strainer 38 retracted and the jacket end 39 is forced into the clay while the sand pump is used to draw in a considerable amount of water. A flow of water arises around the jacket end 39, the speed of flow around the lower edge 40 being very considerable, as described with reference to FIG. I. The large portion of clay 51 is scoured off at its side so that its diameter becomes smaller than the inside diameter of the jacket end 39. The portion of clay 51 is then set up by the strainer 38 exerting a downward pressure thereon (see FIG. 5).

The speed of flow between the upset portion of clay 51 and the jacket end 39 then increases so that consequently the erosion at the outer surface of this portion of clay 51 is increased. The cohesion of the portion of clay 51 is also greatly reduced during upsetting. In the preferred method according to the invention, the bottom edge 40 is continuously introduced more deeply into the firm soil, so that the speed of flow around this lower edge 40 remains considerable. The portion of clay penetrating into the jacket end is also continuously upset or upset with short intervening pauses. In this way the time to insert the suction pipe 33 into the firm soil and hence unproductive time are greatly reduced. With the methods described hereinbefore, the suction pipe 33 can be introduced into the layer of clay either vertically or slantingly.

When the jacket end 39 is beneath the layer of clay 50 in the sand, the location of the strainer 38 in the jacket end 39 is adjusted depending upon the column of soil situated in the breach above the lower edge 40 and depending upon the pressure of the water supplied to the strainer 38 via the three apertures in the throat 42. The concentration of sand in the suspension sucked up is controlled in this way.

When too many large objects have accumulated beneath the strainer 38 in the jacket end 39, the strainer 38 is extended so that the sand can pass inwards through the cylindrical grid 41 (see FIG. 6). Consequently, the suction pressure on the front grid 44 is greatly reduced and large objects can fall away from the front grid 44, this effect being assisted by movements of the suction pipe.

I claim:

1. The method of suction dredging sand from an underwater body of sand covered by a layer of relatively cohesive material such as clay, which comprises the steps of:

a. forcibly inserting the open lower end of a suctiondredging pipe assembly into the layer of cohesive material while flowing ambient water into such lower end, through and out of such assembly at a rate sufficient to entrain at least some of said material;

b. maintaining the flow of ambient water into the lower end of the assembly to form a portion of the material within the lower end thereof, which portion has been scoured away circumferentially by the flowing water to provide clearance between the outer surface of said portion and the inner surface of the assembly;

c. removing the material constituting said portion; and

d. progressively penetrating the lower end of the assembly through said layer according to steps (a), (b) and (c) until the lower end of the assembly has reached the body of sand, the removal of step (c) being effected by periodically withdrawing the lower end of the assembly from said layer while maintaining the flow of ambient water to retain said portion in the assembly, moving the lower end of the assembly to one side and expelling said portion, whereafter the lower end of the assembly is reinserted into the layer essentially along its path of original insertion.

2. The method of suction-dredging sand from an underwater body of sand covered by a layer of relatively cohesive material such as clay, which comprises the steps of:

a. forcibly inserting the open lower end of a suctiondredging pipe assembly into the layer of cohesive material while flowing ambient water into such lower end, through and out of such assembly at a rate sufficient to entrain at least some of said material;

b. maintaining the flow of ambient water into the lower end of the assembly to form a portion of the material within the lower end thereof, which portion has been scoured away circumferentially by the flowing water to provide clearance between the outer surface of said portion and the inner surface of the assembly;

c. removing the material constituting said portion; and

d. progressively penetrating the lower end of the assembly through said layer according to steps (a), (b) and (0) until the lower end of the assembly has reached the body of sand, the removal of step (c) being effected by upsetting said portion by exerting a downward pressure thereon to reduce greatly its adhesion and allow acceleration of its erosion and entrainment by the flowing ambient water.

3. The method according to claim 2 wherein the removal of step (c) is effected by periodically upsetting said portion.

4. The method according to claim 2 wherein the removal of step (c) is effected by continuously upsetting said portion.

5. The method according to claim 2 including the step of introducing ambient water under pressure into the assembly .while establishing flow of sand and water through the lower end thereof after the lower end of the assembly has penetrated the layer of cohesive material.

6. The method according to claim 5 wherein the removal of step (c) is effected by periodically upsetting said portion.

7. The method according to claim 5 wherein the removal of step (c) is effected by continuously upsetting said portion.

8. Suction-dredging apparatus comprising, in combination; suction pipe means adapted for connection to a suction pump for inducting a mixture of sand and water through the lower end of said suction pipe means, said suction pipe means having at least a lower end portion of substantially uniform cross section which is adapted to be inserted into an underwater body of sand;

grid means mounted for movement within said lower end portion of said suction pipe means, said grid means substantially filling the cross section of said lower end portion so as to block the entry of large objects such as stones into that region of said suction pipe means lying above said grid means; and

means for positively moving and locating said grid means within said lower end portion of said suction pipe means.

9. The suction-dredging apparatus as defined in claim 8 wherein said grid means is of cuplike configuration presenting a bottom face surmounted by a cylindrical sidewall, said bottom face and sidewall both being of gridlike form to pass smaller particles such as sand but to block larger objects such as stones or the like; said means for positively moving said grid means having a stroke sufficient to expose said cylindrical sidewall beyond the lower end of said suction pipe means.

10. The suction-dredging apparatus as defined in claim 9 wherein said suction pipe means includes an outer jacket having said lower end portion, an inner pipe fixed within said jacket and located above said lower end portion, and a sliding pipe telescopically cooperating with said inner pipe as an extension thereof, said grid means being fixed to the lower end of said sliding pipe.

11. The suction-dredging apparatus as defined in claim 8 wherein said suction pipe means includes an outer jacket having said lower end portion, an inner pipe fixed within said jacket and located above said lower end portion, and a sliding pipe telescopically cooperating with said inner pipe as an extension thereof, said grid means being fixed to the lower end of said sliding pipe. I 

1. The method of suction dredging sand from an underwater body of sand covered by a layer of relatively cohesive material such as clay, which comprises the steps of: a. forcibly inserting the open lower end of a suction-dredging pipe assembly into the layer of cohesive material while flowing ambient water into such lower end, through and out of such assembly at a rate sufficient to entrain at least some of said material; b. maintaining the flow of ambient water into the lower end of the assembly to form a portion of the material within the lower end thereof, which portion has been scoured away circumferentially by the flowing water to provide clearance between the outer surface of said portion and the inner surface of the assembly; c. removing the material constituting said portion; and d. progressively penetrating the lower end of the assembly through said layer according to steps (a), (b) and (c) until the lower end of the assembly has reached the body of sand, the removal of step (c) being effected by periodically withdrawing the lower end of the assembly from said layer while maintaining the flow of ambient water to retain said portion in the assembly, moving the lower end of the assembly to one side and expelling said portion, whereafter the lower end of the assembly is reinserted into the layer essentially along its path of original insertion.
 2. The method of suction-dredging sand from an underwater body of sand covered by a layer of relatively cohesive material such as clay, which comprises the steps of: a. forcibly inserting the open lower end of a suction-dredging pipe assembly into the layer of cohesive material while flowing ambient water into such lower end, through and out of such assembly at a rate sufficient to entrain at least some of said material; b. maintaining the flow of ambient water into the lower end of the assembly to form a portion of the material within the lower end thereof, which portion has been scoured away circumferentially by the flowing water to provide clearance between the outer surface of said portion and the inner surface of the assembly; c. removing the material constituting said portion; and d. progressively penetrating the lower end of the assembly through said layer according to steps (a), (b) and (c) until the lower end of the assembly has reached the body of sand, the removal of step (c) being effected by upsetting said portion by exerting a downward pressure thereon to reduce greatly its adhesion and allow acceleration of its erosion and entrainment by the flowing ambient water.
 3. The method according to claim 2 wherein the removal of step (c) is effected by periodically upsetting said portion.
 4. The method according to claim 2 wherein the removal of step (c) is effected by continuously upsetting said portion.
 5. The method according to claim 2 including the step of introducing ambient water under pressure into the assembly while establishing flow of sand and water through the lower end thereof after the lower end of the assembly has penetrated the layer of cohesive material.
 6. The method according to claim 5 wherein the removal of step (c) is effected by periodically upsetting said portion.
 7. The method according to claim 5 wherein the removal of step (c) is effected by continuously upsetting said portioN.
 8. Suction-dredging apparatus comprising, in combination; suction pipe means adapted for connection to a suction pump for inducting a mixture of sand and water through the lower end of said suction pipe means, said suction pipe means having at least a lower end portion of substantially uniform cross section which is adapted to be inserted into an underwater body of sand; grid means mounted for movement within said lower end portion of said suction pipe means, said grid means substantially filling the cross section of said lower end portion so as to block the entry of large objects such as stones into that region of said suction pipe means lying above said grid means; and means for positively moving and locating said grid means within said lower end portion of said suction pipe means.
 9. The suction-dredging apparatus as defined in claim 8 wherein said grid means is of cuplike configuration presenting a bottom face surmounted by a cylindrical sidewall, said bottom face and sidewall both being of gridlike form to pass smaller particles such as sand but to block larger objects such as stones or the like; said means for positively moving said grid means having a stroke sufficient to expose said cylindrical sidewall beyond the lower end of said suction pipe means.
 10. The suction-dredging apparatus as defined in claim 9 wherein said suction pipe means includes an outer jacket having said lower end portion, an inner pipe fixed within said jacket and located above said lower end portion, and a sliding pipe telescopically cooperating with said inner pipe as an extension thereof, said grid means being fixed to the lower end of said sliding pipe.
 11. The suction-dredging apparatus as defined in claim 8 wherein said suction pipe means includes an outer jacket having said lower end portion, an inner pipe fixed within said jacket and located above said lower end portion, and a sliding pipe telescopically cooperating with said inner pipe as an extension thereof, said grid means being fixed to the lower end of said sliding pipe. 